In 1881, cooperating with the Rev T J Comber and others, he established a chain of missions at Musuko, Vivi, Isangila, Manyanga, and other points, and in 1884, in a small steam vessel, he explored the Congo to the equator. He established headquarters at Arthington, near Leopoldville, in 1884, and launched on Stanley Pool a river steam vessel, the Peace, in which he explored the Kiva, the Kwango, and the Kasai rivers, discovered the Ruki, or Black River, and ascended the Mubangi for 200 miles to Grenfell Falls, at lat. 4° 40' N. In 1885 he explored with Curt von François other tributaries of the Congo, notably the Busira, along which he found Pygmy Batwa peoples. In the following year he examined the Kasai, the Sankuru, and the Luebo and Lulua, and made careful records of the Bakuba and Bakete tribes. He was awarded in 1887 the Patron's Gold Medal of the Royal Geographical Society for his explorations in the Cameroons and Congo. In 1891 he was appointed a plenipotentiary for Belgium to delimit the boundary line between the Belgian and Portuguese possessions along the Luanda frontier. In 1903 he protested to King Leopold against consistent refusal of the Congo Free State authorities to countenance further Baptist advance beyond Yakusu on the Upper Congo, but with no effect. From 1893 to 1900 Grenfell remained chiefly at Bolobo on the Congo, where a strong mission station was established. After a visit to England in 1900, he started for a systematic exploration of the Aruwimi River and by November 1902 had reached Mawambi, about eighty miles from the western extreme of the Uganda protectorate.
Last years
Between 1903 and 1906 Grenfell was busy with a new station at Yalemba, fifteen miles east of the confluence of the Aruwimi with the Congo. Meanwhile, he found difficulty in obtaining building sites from the Congo Free State, which accorded them freely to Roman Catholics. He grew convinced of the Catholic character of Belgian administration, in which he had previously trusted. In 1903 King Leopold despatched at Grenfell's entreaty a commission of inquiry, before which he gave evidence, but its report gave him little satisfaction. Grenfell died after a bad attack of blackwater fever at Basoko on 1 July 1906. A memorial tablet was unveiled in Heneage Street Baptist Chapel, Birmingham, on 24 September 1907. During major 1950s clearance of the area for redevelopment Heneage Street Baptist was closed. The tablet was recovered and was moved to a new Chapel in north-east Birmingham named in his honour.
